U.S. Bellows, Inc. designed a double hinged reinforced expansion joint for a 92″ diameter pipe in a water treatment plant located in Canada. The bellows, root rings and collars are fabricated from 321 stainless steel. The weld ends and hinge hardware are fabricated from carbon steel. This expansion joint was designed for 100 PSIG at 300°F with 4° angular movement for each bellows. The bellows long seams and longitudinal pipe welds were 100% x-ray examined, and a hydro-test at 150 PSIG, along with a 100% dye penetrant test for all welds was performed prior to shipment.
All bellows have a critical pressure at which they become unstable. Instability can occur in either of two modes, column instability (or squirm), or in-plane deformation of the convolution side wall. Squirm affects the bellows as a whole, while in-plane deformation only affects one or more convolutes individually.
Column Instability Column instability (or squirm), is the phenomena whereby the centerline of a straight bellows develops a sideways or lateral bow. This condition is most associated with bellows which have a relatively large length-to-diameter ration and is analogous to the buckling of a column under compressive load.
In-plane squirm is defined as a shift or rotation of the plane of one or more convolutions such that the plane of these convolutions is no longer perpendicular to the axis of an unreinforced bellows. It is characterized by tilting or warping of one or more convolutions. This condition is predominantly associated with high meridional bending stress and the formation of plastic hinges at the root and crest of the convolutions. It is most common in bellows which have relatively small length-to-diameter ratio.
How to Avoid Instability (or Squirm)
The test pressure should be less than or equal to 1.5 times the design pressure based on column or in-plane stability at ambient temperature material properties.
We recently posted a new page that talks about the dedicated team of employees we have at U.S. Bellows that is working around the clock to serve your expansion joint needs. Go check out their photos and see just how many years of combined experience that the U.S. Bellows team offers! Our U.S. Bellows manager, Mr. John Demusz, who often is the voice behind our expansion joint webinars, is shown below:
U.S. Bellows designed and fabricated a 78″ fabric expansion joint and duct work assembly with a 90° elbow for a sulphuric acid plant in Louisiana. A stress anaylsis was performed to determine thermal movements and spring supports, loads and travel.
The ducts are fabricated from carbon steel and are 30′ long. The expansion joint is designed for 750°F at 5 PSIG with 2.5″ lateral deflection (cold preset) and 2″ axial compression. Cradle supports and a “big ton” spring support were also fabricated for this project.